This invention relates to a thermal transfer recording medium, particularly to a thermal transfer recording medium which is free from occurrence of blocking during storage, without contamination or abrasion of the thermal head during usage and also capable of preventing generation of sticking phenomenon.
As one of techniques concerning thermal recording medium, heat-sensitive paper has been widely known for its ease in handling. For example, Japanese Provisional Patent Publication No. 2795/1982 discloses a technique employing silicon-modified wax together with a binder as the protective layer. However, such a heat-sensitive paper as the recording medium cannot make the printed (recorded) images indelible, but they will readily be color formed by heat or an organic solvent to result in the disadvantage that storability of the printed (recorded) image was poor. In contrast, there is also known a thermal transfer recording medium of the type employing a heat fusible substance as the recording medium excellent in alteration resistance and storability.
Whereas, in the case of such a melt-transfer type thermal transfer recording medium employing a polymeric film such as a polyethyleneterephthalate film as the support, a part of the film support may be melted by a thermal head and stuck through fusion onto the thermal head. This phenomenon is called the sticking phenomenon, which will lower markedly the recording quality and ultimately the film support will be baked onto the thermal head to make delivery of the thermal transfer recording medium no longer possible.
For prevention of this sticking phenomenon, a paper excellent in heat resistance such as condenser paper may be used as the support. However, when such a paper is used, due to poor thermal conductivity from the thermal head, the power applied on the thermal head must be increased, whereby the life of the thermal head will be markedly damaged to a great disadvantage.
On the other hand, there is the technique of employing a backing layer for prevention of the sticking phenomenon. For example, Japanese Provisional Patent Publication No. 7467/1980 proposes to provide a heat-resistant protective film such as of a silicone resin on a film support, but this technique involves the drawback that the heating head is abraded after recording for a long time due to the great friction with the heating head. Also, Japanese Provisional Patent Publication No. 129789/1982 proposes to provide a resin layer containing a surfactant or an organic salt which is solid or meta-solid at room temperature on a film support. This technique involves the drawback that the resin layer absorbs moisture under humid conditions such as during the rainy season, whereby the layer becomes sticky to cause contamination of the heating head. Further, Japanese Provisional Patent Publication No. 187396/1983 discloses a technique for enhancing heat resistance of the backing layer. More specifically, according to this technique, 5 to 40 parts by weight of a compound having diisocyanate or triisocyanate or amino group are added per 100 parts by weight of a thermoplastic resin having --OH group or --COOH group, thereby curing the backing layer through crosslinking. Indeed, this technique is capable of affording sticking resistance, but because of aiming at improvement of heat resistance with the reaction product, difficulties are encountered in manufacturing process and it is not possible to prepare a backing layer with uniform film thickness.
Accordingly, Japanese Provisional Patent Publication No. 171992/1983 proposes to use waxes together with thermoplastic resins, in order to enhance the lubricity of the backing layer. However, when the paraffinic or ethylenic waxes disclosed herein are employed, not only the defect of contamination of head, but also there is the defect of occurrence of blocking during storage of the thermal transfer recording medium. Further, Japanese Provisional Patent Publication No. 155794/1981 proposes to provide a resin layer containing an inorganic pigment having high lubricity on a film support, but this technique involved the drawback that the inorganic pigment peeled off from the resin film and contaminated the thermal head.